One of the notable characteristics of partially or totally fluorinated polymers is their relative low susceptibility to burning and the low level of smoke generated in such situations as compared with other polymers. This characteristic has been utilized in the wire and cable industry, among others, and more specifically in plenum cable constructions and fiber optic cable applications.
Polyvinylidene fluoride homopolymers as well as co-and terpolymers of vinylidene fluoride (PVDF) with other fluorinated monomers such as hexafluoropropylene and tetrafluoroethylene are being used in such applications. Examples of such materials are the various PVDF grades supplied by Pennwalt for these uses under the trademark KYNAR. Other polyfluorinated resins for such applications include fluorinated ethylene propylene (FEP) resin and ethylene-chlorotrifluoroethylene copolymer resin (ECTFE).
Fluoropolymers have LOI (Limiting Oxygen Index) values ranging from the 40's to 90's, as determined by ASTM D-2863. The higher index numbers are achieved by the least flammable polymers. Polyvinylidene fluoride based resins have LOI values in the lower end of that range. In fluoropolymer cable constructions, where both the primary insulation or protective layer and jacket material are composed of fluoropolymer, smoke density and flame spread have generally not been a problem. Such cables are described for example in U.S. Pat. No. 4,401,845. However, is some cable applications and especially in hybrid cable constructions using non-fluoropolymer primary insulation on wires or fiber optic strands in combination with the fluoropolymer jacket encasements, smoke density and/or flame spread problems may occur. Therefore, reducing the smoke density and flame spread properties of the fluorinated polymers and especially PVDF based polymers without significant change in processing properties or in physical properties is a desirable goal. The cable constructions would then exhibit a greater tolerance to the inclusion of non-fluorinated components.
The use of siliceous materials has been reported in patents and other open literature for flame retardation and smoke suppression in various applications such as in polymer foam, fabrics, and building products. Examples of smoke and flame retardation in wire and cable applications include U.S. Pat. No. 4,456,654 disclosing the use of calcium silicate, magnesium silicate and hydrated alumina fillers with an elastomer. U.S. Pat. No. 4,225,649 discloses an aqueous emulsion composition which contains several ingredients including clay. U.S. Pat. No. 4,327,001 discloses cross linked polyolefin jacketing relying mainly on magnesium silicate and alumina hydrate for low smoke characteristics. The addition of molybdates to PVDF has been disclosed for flame and smoke suppression in French Patent Application 2,534,264, but molybdates are relatively expensive.
According to U.S. Pat. No. 3,510,429 a layer of vinylidene polymer containing 2 to 70% by weight of a nonflammable, energy reflective light colored pigment, protects personnel and articles from short term intense thermal radiation such as from an atomic explosion. Among the examples of suitable reflective pigments is aluminum silicate. Dense white smoke evolution is said to occur and aid in the dissipation and attenuation of the intense thermal energy.
I have now found that certain aluminum silicates impart excellent flame and smoke retardant properties to fluorocarbon polymers, which properties are unexpectedly superior when compared to those provided by the use of other siliceous materials.